Electronic image pickup apparatus

ABSTRACT

An electronic image pickup apparatus comprising a zoom lens system and an image pickup device disposed on an image side of the zoom lens system and which converts an image formed by the zoom lens system into an electric signal, the zoom lens system having, in order from an object side, a negative first lens unit, a positive second lens unit, a negative third lens unit, and a positive fourth lens unit, the first lens unit having, in order from the object side, a negative lens and a reflective optical element which reflects an optical path, and during zooming from a wide-angle end to a telephoto end, each space between the lens units which are adjacent with each other being changed, the first lens unit being arranged in a fixed position to the image pickup device, and at least the second lens unit and the third lens unit being moved.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/901,195 filed on Sep. 13, 2007, now U.S. Pat. No. 7,791,817 whichclaims priority to Japanese Application No. 2006-279866 filed on Oct.13, 2006, which is expressly incorporated herein in its entirety byreference thereto.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electronic image pickup apparatus,more particularly, to an electronic image pickup apparatus including azoom lens system having a reflective element.

2. Description of the Related Art

In recent years, instead of a 35 mm silver halide film camera (135formats), a digital camera (an electronic camera) has been a mainstreamwhich photographs a subject by use of an electronic image pickup devicesuch as a CCD image sensor or a CMOS type image sensor. Furthermore, thecamera has a large number of categories in a broad range from a highlyfunctional type for business to a portable popular type.

Especially, in the category of the portable popular type, it has beendemanded that a conveniently usable electronic image pickup apparatus (avideo camera, a digital camera or the like) including a zoom lens systemand having a small size in a depth direction be provided.

The largest problem (bottleneck) which hampers thinning of the camera inthe depth direction is a thickness of an optical system, especially thezoom lens system from a surface closest to an object side to an imagepickup surface. In recent years, as a mainstream of a camera bodythinning technology, a so-called collapsible lens barrel is employed inwhich the optical system projects from a camera body duringphotographing, but the system is stored when carried.

However, in a case where the collapsible lens barrel is employed, muchtime is required for starting the apparatus so as to bring stored lensesinto a usable state, which is unfavorable for usability. When a lensunit closest to the object side is movable, many disadvantages aregenerated from a viewpoint of waterproof or dust-proof design.

In one of constitutions which have been developed in recent years, anoptical path (an optical axis) of the optical system is bent by areflective optical element such as a mirror or a prism so as to providea camera remarkably thin in the depth direction. The constitution isfavorable since, unlike the collapsible lens barrel, a startup time tobring the camera into the usable state (a time to extend the lenses) isnot required and water-proof or dust-proof design may be easilyintroduced.

In the constitution, the lens unit closest to the object side is fixedin a direction along the optical axis, the lens unit is provided withthe reflective optical element, the optical path reflected by theoptical element extends in a vertical or horizontal direction of thecamera body, and a dimension of the electronic image pickup apparatus inthe depth direction is set to be as small as possible.

A zoom lens system in which the optical system capable of achieving thethinning of the apparatus and which is of a positive-lead lens type (thelens unit closest to the object side has a positive refractive power) isdisclosed in, for example, Japanese Patent Application Laid-Open Nos.2004-354,871 and 2004-354,869.

However, such a lens type is constituted so that a composite system of afirst lens unit and a second lens unit has a negative refractive powerin a wide-angle end, but the total length of the whole system easilyincreases. The zoom lens system of the positive-lead lens type islargely influenced by a manufacturing error.

On the other hand, in a zoom lens system of a negative-lead lens type(the lens unit closest to the object side has a negative refractivepower), one lens unit closest to the object side in the wide-angle endhas a negative refractive power, and the total length of the system isadvantageously reduced. It is also known that the system is scarcelyinfluenced by the manufacturing error.

As such a zoom lens system of the negative-lead lens type, a zoom lenssystem is disclosed in Japanese Patent Application Laid-Open No.2005-338,344. This zoom lens system has, in order from the object side,a fixed negative lens unit, a positive lens unit which is movable forzooming, a fixed negative lens unit, and a fourth lens unit which movesalong a track which is convex toward an image surface in order tocompensate an image position.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to an electronic image pickupapparatus comprising a zoom lens system and an image pickup device whichis disposed on an image side of the zoom lens system and which convertsan image formed by the zoom lens system into an electric signal.

Moreover, the zoom lens system includes, in order from an object side, afirst lens unit having a negative refractive power, a second lens unithaving a positive refractive power, a third lens unit having a negativerefractive power and a fourth lens unit having a positive refractivepower.

The first lens unit includes, in order from the object side, a negativelens and a reflective optical element which reflects an optical path.

During zooming from a wide-angle end to a telephoto end, each spacebetween the lens units which are adjacent with each other is changed,but the first lens unit is arranged in a fixed position to the imagepickup device.

According to a first aspect of the present invention, during the zoomingfrom the wide-angle end to the telephoto end, at least the second lensunit and the third lens unit are moved.

According to a second aspect of the present invention, the fourth lensunit includes a single lens having a positive refractive power, and thetotal number of the lenses of the fourth lens unit is one.

According to a third aspect of the present invention, the zoom lenssystem is constituted as a four-unit zoom lens system, the second lensunit includes, in order from the object side, a plurality of positivelenses and a negative lens, and the negative lens is cemented to thepositive lens disposed on the object side of the negative lens.

Other features and advantages of the present invention will becomeapparent from the following detailed description of the embodiments whentaken in conjunction with the accompanying drawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given below and the accompanying drawings, whichare given by way of illustration only and thus are not limitative of thepresent invention, wherein:

FIGS. 1A to 1C are sectional views of Example 1 of a zoom lens systemfor use in an electronic image pickup apparatus of the presentinvention, including an optical axis when focused at infinity, FIG. 1Ais a sectional view of the system in a wide-angle end, FIG. 1B is asectional view of the system in an intermediate position, and FIG. 1C isa sectional view of the system in a telephoto end;

FIGS. 2A to 2C are sectional views of Example 2 of the zoom lens systemfor use in the electronic image pickup apparatus of the presentinvention, including the optical axis when focused at infinity, FIG. 2Ais a sectional view of the system in a wide-angle end, FIG. 2B is asectional view of the system in an intermediate position, and FIG. 2C isa sectional view of the system in a telephoto end;

FIGS. 3A to 3C are sectional views of Example 3 of the zoom lens systemfor use in the electronic image pickup apparatus of the presentinvention, including the optical axis when focused at infinity, FIG. 3Ais a sectional view of the system in a wide-angle end, FIG. 3B is asectional view of the system in an intermediate position, and FIG. 3C isa sectional view of the system in a telephoto end;

FIGS. 4A to 4C are aberration diagrams of Example 1 of the zoom lenssystem when focused at infinity, showing a spherical aberration (SA), anastigmatism (FC), a distortion (DT) and a chromatic aberration ofmagnification (CC), FIG. 4A shows a state of the wide-angle end, FIG. 4Bshows a state of the intermediate position, and FIG. 4C shows a state ofthe telephoto end;

FIGS. 5A to 5C are aberration diagrams of Example 2 of the zoom lenssystem when focused at infinity, showing a spherical aberration (SA), anastigmatism (FC), a distortion (DT) and a chromatic aberration ofmagnification (CC), FIG. 5A shows a state of the wide-angle end, FIG. 5Bshows a state of the intermediate position, and FIG. 5C shows a state ofthe telephoto end;

FIGS. 6A to 6C are aberration diagrams of Example 3 of the zoom lenssystem when focused at infinity, showing a spherical aberration (SA), anastigmatism (FC), a distortion (DT) and a chromatic aberration ofmagnification (CC), FIG. 6A shows a state of the wide-angle end, FIG. 6Bshows a state of the intermediate position, and FIG. 6C shows a state ofthe telephoto end;

FIG. 7 is a diagram showing a basic concept in a case where a distortionof an image is electrically corrected;

FIG. 8 is a diagram showing meaning of a half angle of an object view;

FIG. 9 is a front perspective view showing an appearance of an exampleof a digital camera according to the present invention;

FIG. 10 is a back perspective view of the digital camera of FIG. 9;

FIG. 11 is a schematic diagram showing an inner constitution of thedigital camera of FIG. 9; and

FIG. 12 is a block diagram showing a main part of an inner circuit ofthe digital camera shown in FIG. 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, a zoom lens system for use in an electronic image pickupapparatus according to the present invention will be described.

This zoom lens system includes, in order from an object side, a firstlens unit having a negative refractive power, a second lens unit havinga positive refractive power, a third lens unit having a negativerefractive power and a fourth lens unit having a positive refractivepower. Moreover, the first lens unit includes, in order from the objectside, a negative lens and a reflective optical element which reflects anoptical path.

During zooming from a wide-angle end to a telephoto end, each spacebetween the lens units which are adjacent with each other is changed,but the first lens unit is arranged in a fixed position to an imagepickup device.

When the first lens unit is provided with the negative refractive power,a diameter of the first lens unit can be reduced. When the first lensunit includes the reflective optical element, an effective diameter ofoptical elements disposed behind the reflective optical element can bereduced. Moreover, a thickness of an electronic image pickup apparatusin a depth direction can be reduced.

Moreover, in a case where the second lens unit is a positive lens unitand the third lens unit is a negative lens unit, these second and thirdlens units constitute an optical system of a telephoto type in which thepositive refractive power and the negative refractive power arearranged. According to this constitution, a front-side principal pointof a composite optical system of the second lens unit and the third lensunit can be positioned close to the first lens unit. Therefore, since aspace between the principal points of the first lens unit and thecomposite optical system of the second and third lens units can bereduced, the total length of the zoom lens system can be reduced.

Moreover, in an arrangement in which the fourth lens unit is a positivelens unit, a ray which enters the image pickup device can come close toa state vertical to an image pickup surface, telecentricity can besecured, and deterioration of an image can easily be suppressed.

In the above-mentioned lens constitution, it is preferable that thesecond and third lens units are moved during the zooming to perform thezooming and compensate a change of an image surface position due to thezooming.

In such a lens unit movement system, the fourth lens unit can be simplyfixed or slightly moved to perform the zooming. Therefore, a spacebetween the fourth lens unit and an image surface can be reduced, andthis is advantageous in reducing the total length of the zoom lenssystem.

Moreover, it is preferable that the zoom lens system has an aperturestop which moves integrally with the second lens unit. In consequence, adiameter of each lens in the second lens unit and lenses disposed afterthe second lens unit can be reduced, and this is further advantageousfor miniaturization.

It is preferable that the fourth lens unit is constituted of a singlelens having a positive refractive power, and is provided with a functionof a field lens. This field lens contributes to securement of thetelecentricity. This function is satisfactorily fulfilled by only thesingle lens having the positive refractive power, and such a one-lensconstitution is also preferable for achieving the miniaturization.

It is more preferable that the fourth lens unit includes one positivelens component having an aspherical surface. This constitution isadvantageous for correction of an astigmatism, regulation of an exitpupil position and the miniaturization.

It is preferable that the second lens unit includes, in order from theobject side, a plurality of positive lenses and a negative lens, and thenegative lens is cemented to the positive lens disposed on the objectside of the negative lens.

When the second lens unit has the above-mentioned constitution, thepositive refractive power of the second lens unit can be shared by theplurality of positive lenses. When the negative lens is disposed,aberrations can easily be cancelled by the negative lens and thepositive lenses. Since this negative lens is cemented to the object-sidepositive lens, a chromatic aberration is easily corrected, and aninfluence of relative eccentricity between the lenses having strongpowers is easily suppressed.

The second lens unit is a lens unit having a zooming function, butaccording to the above-mentioned constitution, even if the refractivepower of the second lens unit is increased, the aberrations are easilycorrected, and the total length of the zoom lens system isadvantageously reduced.

Moreover, when the lenses are arranged in the above-mentioned order, adivergent light flux from the first lens unit is gradually converged bya plurality of positive lens. Afterward, the negative lens is arranged,and a front-side principal point of the second lens unit can thereforebe positioned close to the object side. In consequence, a zoom ratio isadvantageously secured with respect to a movement amount, and the systemis further advantageously miniaturized. A coma and a curvature of fieldare advantageously corrected.

Especially, it is preferable that the second lens unit has at least apositive lens and a cemented lens constituted by cementing a positivelens and a negative lens in order from the object side.

It is preferable that the reflective optical element disposed in thefirst lens unit includes a prism having a reflective surface.

When the reflective optical element is constituted as a prism, anoptical path length can be reduced, an entrance pupil can therefore beset to be shallow, a lens diameter can be reduced, and a length of theprism can be reduced.

It is preferable that the above-mentioned zoom lens system satisfies thefollowing condition:0.4<f ₂ /f ₁<0.8  (1),in which f₂ is a focal length of the second lens unit, and f₁ is a focallength of the zoom lens system in the telephoto end.

The condition (1) appropriately defines the refractive power of thesecond lens unit.

In a case where f₂/f₁ is not above an upper limit of the condition (1)so that the positive refractive power of the second lens unit issecured, the movement amount of the second lens unit can be suppressed,and the system is further advantageously miniaturized.

In a case where f₂/f₁ is not below a lower limit of the condition (1) sothat the positive refractive power of the second lens unit isappropriately suppressed, the generation of the aberration can besuppressed, and especially the curvature of field can advantageously becorrected.

Moreover, it is preferable that the zoom lens system satisfies thefollowing condition:1.5<|f ₁ /f _(w)|<3.0  (2),in which f₁ is a focal length of the first lens unit, and f_(w) is afocal length of the zoom lens system in the wide-angle end.

The condition (2) appropriately defines the refractive power of thefirst lens unit.

When |f₁/f_(w)| is not above an upper limit of the condition (2), theentrance pupil can be inhibited from being deepened (a distance from anincidence surface to the entrance pupil can be inhibited from beingincreased), and a diameter of the negative lens of the first lens unitis easily prevented from being increased. A size of the reflectivesurface of the reflective optical element is easily reduced.

When |f₁/f_(w)| is not below a lower limit of the condition (2), adistortion and the curvature of field are easily inhibited from beingexcessively increased.

Moreover, it is preferable that the zoom lens system satisfies thefollowing condition:1.0<|f _(L1) /f _(w)|<2.0  (3),in which f_(L1) is a focal length of the negative lens of the first lensunit closest to the object side, and f_(w) is a focal length of the zoomlens system in the wide-angle end.

The condition (3) appropriately defines the refractive power of thenegative lens of the first lens unit. To set the entrance pupil to beshallow (reduce the distance between the incidence surface and theentrance pupil) so that the optical path can be reflected, therefractive power of the negative lens of the first lens unit may beincreased.

When |f_(L1)/f_(w)| is not above an upper limit of the condition (3),the refractive power of the negative lens is secured, and the entrancepupil is easily set to be shallow. Therefore, even if an angle of viewis secured, diameters and sizes of optical elements (the lenses and thereflective optical element) constituting the first lens unit are easilyinhibited from being increased, and the reflective optical element iseasily arranged.

When the second lens unit following the first lens unit is moved, a zoomratio is easily obtained. While the movement amount of the second lensunit is reduced, the zoom ratio is easily secured.

In a case where |f_(L1)/f_(w)| is not below a lower limit of thecondition (3), an off-axial aberration such as the distortion easilygenerated in the negative lens in which an incident ray height easilyincreases and a chromatic aberration are advantageously corrected.

Moreover, in the above-mentioned zoom lens system, in a case where thethird lens unit is moved during the zooming from the wide-angle end tothe telephoto end, it is preferable that the third lens unit movestoward the object side and then reverses a movement direction thereof tomove toward the image surface.

When the third lens unit is moved as described above, the total lengthof the zoom lens system is advantageously reduced. Moreover, the thirdlens unit can be provided with a function of compensating a position ofthe image surface. Furthermore, the curvature of field is advantageouslycorrected.

Moreover, it is more preferable to move the third lens unit so that theunit is arranged closer to the object side in the telephoto end than inthe wide-angle end. In consequence, the third lens unit is also easilyprovided with a zooming function, and a balance between theminiaturization and the securing of the zoom ratio is easilyestablished.

Furthermore, it is more preferable that during the zooming from thewide-angle end to the telephoto end, the second lens unit moves towardthe only object side, the third lens unit moves toward the object side,and then moves toward the image surface, the fourth lens unit isarranged in a fixed position to the image pickup device, and the secondlens unit moves via a state in which the unit has a magnification of −1.

According to the above-mentioned movement system of the lens unit, thesecond lens unit is easily provided with a main zooming function whilesuppressing the total length of the zoom lens system. Moreover, thethird lens unit can be provided with a function of compensating afluctuation of an image position due to the zooming. The third lens unitmoves along a track so as to be positioned closest to the object side inthe vicinity of the state in which the second lens unit has themagnification of −1.

To provide the fourth lens unit with a function of compensating afluctuation of the image position, the fourth lens unit needs to bemoved along a track which is convex toward the image side. Therefore, itis difficult to reduce the space between the fourth lens unit and theimage pickup device. When the third lens unit is moved as describedabove, a space where the lens units are to be arranged is advantageouslyreduced.

It is preferable that the third lens unit is constituted of one singlelens having a negative refractive power.

When the third lens unit includes the minimum number of the lenses so asto have the function of compensating the fluctuation of the imageposition, the zoom lens system is easily miniaturized.

It is preferable that the aperture stop of the zoom lens system isarranged immediately before the second lens unit on the object side andmoved integrally with the second lens unit. In this case, it is morepreferable that the second lens unit includes, in order from the objectside, two positive lenses whose convex surfaces face the object side, apositive lens and a negative lens whose concave surface faces the imageside.

The aperture stop is integrated with the second lens unit to reduce aneffective diameter of the second lens unit in which the refractive powereasily increases, and both of the miniaturization and the securement ofthe refractive power are advantageously realized.

At this time, when the second lens unit is constituted as describedabove, the light flux from the first lens unit is gradually converged bythe plurality of positive lenses, and an off-axial light flux isrefracted in such a direction as to come away from the optical axis bythe negative lens closest to the image side, so that a size of thesecond lens unit can be set to be small with respect to that of theimage surface.

Moreover, a principal point of the second lens unit itself can bedisposed close to the first lens unit, and the zoom ratio isadvantageously secured with respect to the movement amount of the secondlens unit.

It is more preferable that the third lens unit has a negative lenscomponent whose concave surface faces the image side so as to satisfythe following condition:1.0<(R ₁ +R ₂)/(R ₁ −R ₂)<3.0  (4),in which R₁ is a paraxial radius of curvature of an object-side surfaceof the negative lens component, and R₂ is a paraxial radius of curvatureof an image-side surface of the negative lens component. Here, the lenscomponent is a lens having only two surfaces of the object-side surfaceand the image-side surface which come in contact with air in the opticalpath, and is a single lens or a cemented lens.

The condition (4) appropriately defines a shape of the negative lenscomponent included in the third lens unit.

When (R₁+R₂)/(R₁−R₂) is not above an upper limit of the condition (4),the third lens unit is easily arranged close to the object side withrespect to the principal point, and the diameter is advantageouslyreduced. Moreover, generation of the aberration at the center of theimage surface is easily suppressed.

When (R₁+R₂)/(R₁−R₂) is not below a lower limit of the condition (4),the paraxial radius of curvature of the negative lens component isinhibited from being excessively reduced; and the curvature of field iseasily corrected.

Furthermore, it is more preferable that the third lens unit includes theonly negative lens component, the image-side surface of the second lensunit is a concave surface, and the object-side surface of the fourthlens unit is a convex surface.

According to such a constitution, curvatures of lens surfaces of thesecond and third lens units which face each other, and curvatures oflens surfaces of the third and fourth lens units which face each otherhave the same signs, respectively, the fourth lens unit itself canfurther be thinned, and the system is advantageously miniaturized. Inaddition, the aberration fluctuation during the zooming is easilysuppressed. Also in this respect, it is preferable to satisfy the abovecondition (4).

Moreover, it is preferable that the first lens unit has one positivelens and one negative lens on the image side of the reflective opticalelement. In consequence, the chromatic aberration and the like of thefirst lens unit are advantageously corrected, and a size of the firstlens unit is advantageously reduced.

Moreover, it is more preferable to set the above-mentioned conditions asfollows. In consequence, the above-mentioned effects can further beproduced.

It is more preferable to set an upper limit value of the condition (1)to 0.7, and it is more preferable to set a lower limit value to 0.5.

It is more preferable to set an upper limit value of the condition (2)to 2.5, and it is more preferable to set a lower limit value to 1.8.

It is more preferable to set an upper limit value of the condition (3)to 1.9, and it is more preferable to set a lower limit value to 1.5.

It is more preferable to set an upper limit value of the condition (4)to 2.5, and it is more preferable to set a lower limit value to 1.5.

Moreover, it is preferable that the above-mentioned zoom lens system isconstituted as a four-unit zoom lens system, that is, as a zoom lenssystem which does not have any lens unit after the fourth lens unit, sothat the total length of the system is reduced.

Next, numerical examples of the zoom lens system will be described.

FIGS. 1A to 3C are sectional views of Numerical Examples 1 to 3including an optical axis when focused at infinity. FIGS. 1A, 2A and 3Aare sectional views in a wide-angle end, FIGS. 1B, 2B and 3B aresectional views in an intermediate position, and FIGS. 1C, 2C and 3C aresectional views in a telephoto end. In FIGS. 1A to 3C, G1 is a firstlens unit, G2 is a second lens unit, S is an aperture stop, G3 is athird lens unit, G4 is a fourth lens unit, a parallel flat plate F is alow pass filter provided with a wavelength band restrictive coatingwhich limits an infrared ray, a parallel flat plate C is a cover glassof an electronic image pickup device, and I is an image surface. It isto be noted that the surface of the cover glass C may be provided with amultilayered thin film for limiting a wavelength band. The cover glass Cmay be provided with a function of the low pass filter. The parallelflat plate P of the first lens unit G1 is development of an optical pathbending prism. A reflective surface is positioned in the middle of athird surface and a fourth surface described later in lens data. It isto be noted that as the optical path bending prism P, a reflective prismwhich bends the optical path as much as 90° as shown in FIG. 11 is usedin many cases, but another reflective prism may be used.

A zoom lens system shown in FIGS. 1A to 1C includes, in order from anobject side, a first lens unit G1 having a negative refractive power, anaperture stop S, a second lens unit G2 having a positive refractivepower, a third lens unit G3 having a negative refractive power and afourth lens unit G4 having a positive refractive power.

During zooming from a wide-angle end to a telephoto end, the first lensunit G1 is fixed, the second lens unit G2 moves toward the object side,the third lens unit G3 once moves toward the object side and thenreverses a movement direction thereof to move toward an image side, andthe fourth lens unit G4 is fixed.

The first lens unit G1 includes, in order from the object side, a firstnegative meniscus lens whose concave surface faces the image side, anoptical path bending prism P, a second double-concave negative lens, anda third positive meniscus lens whose convex surface faces the objectside. The second double-concave negative lens is cemented to the thirdpositive meniscus lens. The second lens unit G2 includes, in order fromthe object side, a fourth double-convex positive lens, a fifthdouble-convex positive lens, a sixth positive meniscus lens whoseconcave surface faces the object side, and a seventh double-concavenegative lens. The sixth positive meniscus lens is cemented to theseventh double-concave negative lens. The third lens unit G3 includes aneighth negative meniscus lens whose convex surface faces the objectside. The fourth lens unit G4 includes a ninth double-convex positivelens.

Aspherical surfaces are used on five surfaces including an image-sidesurface of the first negative meniscus lens, opposite surfaces of thefourth double-convex positive lens, and opposite surfaces of the ninthdouble-convex positive lens.

A zoom lens system shown in FIGS. 2A to 2C includes, in order from anobject side, a first lens unit G1 having a negative refractive power, anaperture stop S, a second lens unit G2 having a positive refractivepower, a third lens unit G3 having a negative refractive power and afourth lens unit G4 having a positive refractive power.

During zooming from a wide-angle end to a telephoto end, the first lensunit G1 is fixed, the second lens unit G2 moves toward the object side,the third lens unit G3 once moves toward the object side, and reverses amovement direction thereof to move toward an image side and the fourthlens unit G4 is fixed.

The first lens unit G1 includes, in order from the object side, a firstnegative meniscus lens whose concave surface faces the image side, anoptical path bending prism P, a second double-concave negative lens anda third positive meniscus lens whose convex surface faces the objectside. The second double-concave negative lens is cemented to the thirdpositive meniscus lens. The second lens unit G2 includes, in order fromthe object side, a fourth double-convex positive lens, a fifthdouble-convex positive lens, a sixth positive meniscus lens whoseconcave surface faces the object side and a seventh double-concavenegative lens. The sixth positive meniscus lens is cemented to theseventh double-concave negative lens. The third lens unit G3 includes aneighth negative meniscus lens whose convex surface faces the objectside. The fourth lens unit G4 includes a ninth double-convex positivelens.

Aspherical surfaces are used on five surfaces including an image-sidesurface of the first negative meniscus lens, opposite surfaces of thefourth double-convex positive lens and opposite surfaces of the ninthdouble-convex positive lens.

A zoom lens system shown in FIGS. 3A to 3C includes, in order from anobject side, a first lens unit G1 having a negative refractive power, anaperture stop S, a second lens unit G2 having a positive refractivepower, a third lens unit G3 having a negative refractive power and afourth lens unit G4 having a positive refractive power.

During zooming from a wide-angle end to a telephoto end, the first lensunit G1 is fixed, the second lens unit G2 moves toward the object side,the third lens unit G3 once moves toward the object side, and reverses amovement direction thereof to move toward an image side, and the fourthlens unit G4 is fixed.

The first lens unit G1 includes, in order from the object side, a firstnegative meniscus lens whose concave surface faces the image side, anoptical path bending prism P, a second double-concave negative lens anda third positive meniscus lens whose convex surface faces the objectside. The second double-concave negative lens is cemented to the thirdpositive meniscus lens. The second lens unit G2 includes a fourthdouble-convex positive lens, a fifth double-convex positive lens, asixth positive meniscus lens whose concave surface faces the object sideand a seventh double-concave negative lens. The sixth positive meniscuslens is cemented to the seventh double-concave negative lens. The thirdlens unit G3 includes an eighth negative meniscus lens whose convexsurface faces the object side. The fourth lens unit G4 includes a ninthdouble-convex positive lens.

Aspherical surfaces are used on five surfaces including an image-sidesurface of the first negative meniscus lens, opposite surfaces of thefourth double-convex positive lens and opposite surfaces of the ninthdouble-convex positive lens.

Next, numerical data of the above zoom lens systems will be described.In addition to the above symbols, f is a focal length of a zoom lenssystem, F_(NO) is the F-number, ω is a half angle of view, WE is awide-angle end, ST is an intermediate position, TE is a telephoto end,r₁, r₂, . . . are paraxial radii of curvatures of lens surfaces, d₁, d₂,are spaces between the lens surfaces, n_(d1), n_(d2), . . . arerefractive indices of lenses for the d-line, and v_(d1), v_(d2), . . .are the Abbe numbers of the lenses. Symbol (AS) after the radius ofcurvature indicates that the surface is an aspherical surface, (S)indicates that the surface is an aperture stop surface, and (I)indicates that the surface is an image surface, respectively. A shape ofthe aspherical surface is represented by the following equation in acoordinate system in which an optical axis is an x-axis (it is assumedthat a light traveling direction is a positive direction), anintersection between the optical axis and the aspherical surface is anorigin, and a direction passing through the origin and crossing theoptical axis at right angles is a y-axis.x=(y ² /r)/[1+{1−(K+1)(y/r)²}^(1/2) ]+A ₄ y ⁴ +A ₆ y ⁶ +A ₈ y ⁸ +A ₁₀ y¹⁰ +A ₁₂ y ¹²,in which r is a paraxial radius of curvature, K is a conic constant, andA₄, A₆, A₈, A₁₀ and A₁₂ are 4-th, 6-th, 8-th, 10-th and 12-th orderaspherical coefficients. In the aspherical surface coefficient, “e-n” (nis an integer) indicates “×10 ^(−n)”.

Numerical Example 1

r₁ = 37.208 d₁ = 1.00 n_(d1) = 1.85135 ν_(d1) = 40.10 r₂ = 6.337(AS) d₂= 3.10 r₃ = ∞ d₃ = 7.80 n_(d2) = 1.83481 ν_(d2) = 42.71 r₄ = ∞ d₄ = 0.20r₅ = −1172.817 d₅ = 0.66 n_(d3) = 1.49700 ν_(d3) = 81.54 r₆ = 10.191 d₆= 1.69 n_(d4) = 1.90366 ν_(d4) = 31.31 r₇ = 29.145 d₇ = variable r₈ =∞(S) d₈ = 0.75 r₉ = 11.445(AS) d₉ = 3.16 n_(d5) = 1.59201 ν_(d5) = 67.02r₁₀ = −14.097(AS) d₁₀ = 0.10 r₁₁ = 7.662 d₁₁ = 2.00 n_(d6) = 1.72916ν_(d6) = 54.68 r₁₂ = −47.575 d₁₂ = 0.10 r₁₃ = −291.192 d₁₃ = 1.51 n_(d7)= 1.88300 ν_(d7) = 40.76 r₁₄ = −10.276 d₁₄ = 0.66 n_(d8) = 1.90366ν_(d8) = 31.31 r₁₅ = 4.480 d₁₅ = variable r₁₆ = 36.574 d₁₆ = 0.70 n_(d9)= 1.80400 ν_(d9) = 46.57 r₁₇ = 14.427 d₁₇ = variable r₁₈ = 10.155(AS)d₁₈ = 3.55 n_(d10) = 1.58913 ν_(d10) = 61.25 r₁₉ = −14.054(AS) d₁₉ =0.50 r₂₀ = ∞ d₂₀ = 0.50 n_(d11) = 1.54771 ν_(d11) = 62.84 r₂₁ = ∞ d₂₁ =0.50 r₂₂ = ∞ d₂₂ = 0.50 n_(d12) = 1.51633 ν_(d12) = 64.14 r₂₃ = ∞ d₂₃ =0.37 r₂₄ = ∞(I) Aspherical coefficient 2nd surface r = 6.337 K = 0.000A₄ = −1.68882e−04 A₆ = −4.89187e−06 A₈ = −4.47919e−08 A₁₀ = 2.02995e−09A₁₂ = −1.74477e−10 9th surface r = 11.445 K = 0.000 A₄ = −2.99481e−04 A₆= −1.32415e−05 A₈ = 6.10010e−07 A₁₀ = −3.03819e−08 10th surface r =−14.097 K = 0.000 A₄ = 1.74109e−05 A₆ = −6.71330e−06 A₈ = 1.81593e−07A₁₀ = −1.56812e−08 18th surface r = 10.155 K = 0.000 A₄ = −9.25614e−04A₆ = 7.45283e−05 A₈ = −3.13454e−06 A₁₀ = 2.89740e−08 19th surface r =−14.054 K = 0.000 A₄ = −2.05197e−03 A₆ = 2.92360e−04 A₈ = −1.69661e−05A₁₀ = 4.22694e−07 A₁₂ = −4.07295e−09 Zoom Data (∞) WE ST TE f(mm) 5.079.58 17.37 F_(NO) 3.30 4.50 5.09 2ω(°) 80.83 44.00 24.46 d₇ 16.58 8.941.98 d₁₅ 3.27 2.93 16.25 d₁₇ 3.90 11.88 5.52

Numerical Example 2

r₁ = 37.232 d₁ = 1.00 n_(d1) = 1.85135 ν_(d1) = 40.10 r₂ = 6.345(AS) d₂= 3.08 r₃ = ∞ d₃ = 7.80 n_(d2) = 1.83481 ν_(d2) = 42.71 r₄ = ∞ d₄ = 0.20r₅ = −1122.538 d₅ = 0.66 n_(d3) = 1.49700 ν_(d3) = 81.54 r₆ = 10.192 d₆= 1.70 n_(d4) = 1.90366 ν_(d4) = 31.31 r₇ = 29.093 d₇ = variable r₈ =∞(S) d₈ = 0.75 r₉ = 11.448(AS) d₉ = 3.19 n_(d5) = 1.59201 ν_(d5) = 67.02r₁₀ = −14.103(AS) d₁₀ = 0.10 r₁₁ = 7.659 d₁₁ = 2.00 n_(d6) = 1.72916ν_(d6) = 54.68 r₁₂ = −47.547 d₁₂ = 0.10 r₁₃ = −288.469 d₁₃ = 1.51 n_(d7)= 1.88300 ν_(d7) = 40.76 r₁₄ = −10.239 d₁₄ = 0.66 n_(d8) = 1.90366ν_(d8) = 31.31 r₁₅ = 4.484 d₁₅ = variable r₁₆ = 36.590 d₁₆ = 0.70 n_(d9)= 1.80400 ν_(d9) = 46.57 r₁₇ = 14.378 d₁₇ = variable r₁₈ = 10.143(AS)d₁₈ = 3.55 n_(d10) = 1.58913 ν_(d10) = 61.25 r₁₉ = −13.943(AS) d₁₉ =0.50 r₂₀ = ∞ d₂₀ = 0.50 n_(d11) = 1.54771 ν_(d11) = 62.84 r₂₁ = ∞ d₂₁ =0.50 r₂₂ = ∞ d₂₂ = 0.50 n_(d12) = 1.51633 ν_(d12) = 64.14 r₂₃ = ∞ d₂₃ =0.37 r₂₄ = ∞(I) Aspherical coefficient 2nd surface r = 6.345 K = 0.000A₄ = −1.65289e−04 A₆ = −4.88389e−06 A₈ = −2.32910e−08 A₁₀ = 8.96908e−10A₁₂ = −1.50387e−10 9th surface r = 11.448 K = 0.000 A₄ = −2.97053e−04 A₆= −1.26024e−05 A₈ = 6.30126e−07 A₁₀ = −3.04937e−08 10th surface r =−14.103 K = 0.000 A₄ = 2.22265e−05 A₆ = −6.38515e−06 A₈ = 2.15120e−07A₁₀ = −1.62773e−08 18th surface r = 10.143 K = 0.000 A₄ = −8.93052e−04A₆ = 7.24554e−05 A₈ = −2.87069e−06 A₁₀ = 2.33783e−08 19th surface r =−13.943 K = 0.000 A₄ = −1.99543e−03 A₆ = 2.91865e−04 A₈ = −1.65663e−05A₁₀ = 3.97965e−07 A₁₂ = −3.65767e−09 Zoom Data (∞) WE ST TE f(mm) 5.079.58 17.39 F_(NO) 3.30 4.50 5.10 2ω(°) 80.95 44.02 24.44 d₇ 16.56 8.921.97 d₁₅ 3.25 2.93 16.23 d₁₇ 3.91 11.86 5.52

Numerical Example 3

r₁ = 37.875 d₁ = 1.00 n_(d1) = 1.85135 ν_(d1) = 40.10 r₂ = 6.325(AS) d₂= 3.10 r₃ = ∞ d₃ = 7.80 n_(d2) = 1.83481 ν_(d2) = 42.71 r₄ = ∞ d₄ = 0.20r₅ = 1354.124 d₅ = 0.66 n_(d3) = 1.49700 ν_(d3) = 81.54 r₆ = 10.228 d₆ =1.72 n_(d4) = 1.90366 ν_(d4) = 31.31 r₇ = 29.207 d₇ = variable r₈ = ∞(S)d₈ = 0.75 r₉ = 11.431(AS) d₉ = 3.25 n_(d5) = 1.59201 ν_(d5) = 67.02 r₁₀= −14.592(AS) d₁₀ = 0.10 r₁₁ = 7.477 d₁₁ = 2.00 n_(d6) = 1.74100 ν_(d6)= 52.64 r₁₂ = −49.707 d₁₂ = 0.10 r₁₃ = −173.749 d₁₃ = 1.51 n_(d7) =1.88300 ν_(d7) = 40.76 r₁₄ = −9.286 d₁₄ = 0.66 n_(d8) = 1.90366 ν_(d8) =31.31 r₁₅ = 4.418 d₁₅ = variable r₁₆ = 49.887 d₁₆ = 0.70 n_(d9) =1.80400 ν_(d9) = 46.57 r₁₇ = 16.178 d₁₇ = variable r₁₈ = 10.157(AS) d₁₈= 3.57 n_(d10) = 1.58913 ν_(d10) = 61.25 r₁₉ = −12.911(AS) d₁₉ = 0.50r₂₀ = ∞ d₂₀ = 0.50 n_(d11) = 1.54771 ν_(d11) = 62.84 r_(2l) = ∞ d₂₁ =0.50 r₂₂ = ∞ d₂₂ = 0.50 n_(d12) = 1.51633 ν_(d12) = 64.14 r₂₃ = ∞ d₂₃ =0.37 r₂₄ = ∞(I) Aspherical coefficient 2nd surface r = 6.325 K = 0.000A₄ = −1.80433e−04 A₆ = −6.62233e−07 A₈ = −4.72215e−07 A₁₀ = 1.86810e−08A₁₂ = −3.99354e−10 9th surface r = 11.431 K = 0.000 A₄ = −2.48988e−04 A₆= −9.02312e−06 A₈ = 4.37993e−07 A₁₀ = −2.13163e−08 10th surface r =−14.592 K = 0.000 A₄ = 5.94815e−05 A₆ = −5.56616e−06 A₈ = 2.19551e−07A₁₀ = −1.34713e−08 18th surface r = 10.157 K = 0.000 A₄ = −1.11958e−03A₆ = 8.51909e−05 A₈ = −2.98901e−06 A₁₀ = 2.01912e−08 19th surface r =−12.911 K = 0.000 A₄ = −2.72379e−03 A₆ = 3.73308e−04 A₈ = −2.00079e−05A₁₀ = 4.70692e−07 A₁₂ = −4.35154e−09 Zoom Data (∞) WE ST TE f(mm) 5.079.55 17.38 F_(NO) 3.30 4.50 5.10 2ω(°) 80.73 44.05 24.42 d₇ 16.63 8.991.98 d₁₅ 3.24 2.93 16.30 d₁₇ 3.92 11.88 5.53

FIGS. 4A to 6C show aberration diagrams of Numerical Examples 1 to 3when focused at infinity, respectively. In these aberration drawings,FIGS. 4A, 5A and 6A show a spherical aberration (SA), an astigmatism(FC), a distortion (DT) and a chromatic aberration (CC) of magnificationin a wide-angle end, FIGS. 4B, 5B and 6B show the aberrations in anintermediate position, and FIGS. 4C, 5C and 6C show the aberrations in atelephoto end. In the drawings, ω is a half angle of view.

Next, values of the conditions (1) to (4) of the numerical examples willbe described.

Numerical Numerical Numerical Conditions Example 1 Example 2 Example 3(1) f₂/f₁ 0.65 0.65 0.65 (2) |f₁/f_(w)| 2.08 2.08 2.09 (3)|f_(L1)/f_(w)| 1.8 1.8 1.78 (4) (R₁ + R₂)/(R₁ − R₂) 2.30 2.29 1.96

To miniaturize a zoom lens system and increase a zoom ratio, it ispreferable to enlarge a negative refractive power of a first lens unit.However, in this case, a barrel-type distortion in the vicinity of thewide-angle end is easily generated. Therefore, in a case where anelectronic image pickup apparatus is provided with a processing sectionwhich processes a signal from an image pickup device to correct thedistortion of the zoom lens system, the electronic image pickupapparatus is further advantageously miniaturized and provided with ahigh performance.

Next, a basic concept will be described in a case where the distortiongenerated in an optical system is electrically corrected using an imageprocessing technology in the electronic image pickup apparatus. In thefollowing description, such a technique is referred to as digitalcorrection of the distortion of an image.

As shown in FIG. 7, a circle which comes in contact with long sides ofan effective image pickup surface ES having the center on anintersection between an optical axis Lc and the image pickup surface andwhich has a radius R (an image height R) is considered. Magnificationsat points on the circumference of this circle are fixed, andcircumferential points are regarded as references for the correction.Moreover, other circumferential points on an arbitrary radius r(ω) (theimage height r(ω)) are moved in a substantially radial direction, andare concentrically moved so as to provide a radius r′(ω). Inconsequence, the distortion of the optical image is corrected. Forexample, in FIG. 7, a point P₁ positioned inwardly from the circlehaving the radius R on a circumference of an arbitrary radius r₁(ω) ismoved to a point P₂ on a circumference of the radius r′(ω) inwardlytoward the center of the circle. A point Q₁ positioned on acircumference of an arbitrary radius r₂(ω) outside the circle having theradius R is moved to a point Q₂ on a circumference of a radius r₂′(ω)away from the center of the circle. Here, the radius r′(ω) can berepresented as follows:r′(ω)=α·f·tan ω (0≦α≦1),in which ω is a half angle of an object view, and f is a focal length ofan image forming optical system (the zoom lens system in this example).Here, as shown in FIG. 8, the half angle of the object view is an anglebetween the optical axis Lc and a chief ray CR from an object point Ocorresponding to an image point M formed at a position of a height r′(ω)from the center of the image pickup surface.

Here, assuming that an ideal image height corresponding to a point onthe circumference of the radius R (the image height R) is Y, thefollowing equation results:α=R/Y=R/(f·tan ω).

Ideally, the optical system is rotationally symmetric with respect tothe optical axis. Therefore, the distortion is also rotationallysymmetrically generated with respect to the optical axis. In a casewhere the optically generated distortion is electrically corrected, ifthe distortion can be corrected using symmetry with respect to theoptical axis as described above, the correction is advantageous inrespect of a data amount and a calculation amount.

However, when the optical image is photographed with an electronic imagepickup device, the image is not represented by a continuous amount dueto sampling by pixels of the image pickup device. Therefore, the circleof the radius R virtually drawn on the optical image is not a strictlycorrect circle, if the pixels are not radially arranged on the imagepickup surface of the electronic image pickup device. That is, tocorrect a shape of an image given as an aggregate of data obtained fromdiscrete coordinate points (the pixels of the electronic image pickupdevice), the circle having the magnification fixed as described abovedoes not actually exist. Therefore, it is preferable to use a method ofdetermining a moved coordinate (X_(i)′, Y_(j)′) for each pixel(coordinate (X_(i), Y_(j))). It is to be noted that when a plurality ofpixels move to a position of one coordinate (X_(i)′, Y_(j)′), an averagevalue of values of the pixels is obtained as data of the pixels atpositions of the coordinate (X_(i)′, Y_(j)′). Moreover, data of aposition where any point does not come is prepared by interpolationusing data of several surrounding pixels having data generated by themovements of the pixels.

Especially, in an electronic image pickup apparatus of the zoom lenssystem, such a method is effective for the correction in a case wherethe point of the optical image in which the magnification should befixed does not exist on the circumference having the center on theoptical axis, and the circle of the radius R drawn on the optical imageis asymmetric due to manufacturing errors and the like of the opticalsystem and the electronic image pickup device.

In the electronic image pickup apparatus in which such correction isperformed, to calculate a correction amount r′(ω)−r(ω), data indicatinga relation between the half angle ω of the object view and the imageheight r, or data indicating a relation between the actual image heightr and an ideal image height r′ and α may be recorded in a recordingmedium incorporated in the electronic image pickup apparatus.

It is to be noted that the radius R may satisfy the following conditionso that a light quantity does not excessively fall short at oppositeends of the image in a short-side direction, after the distortion of theimage has been corrected.0≦R≦0.6L _(S),in which L_(s) is a length of the short side of the effective imagepickup surface.

The radius R preferably satisfies the following condition.0.3L _(S) ≦R≦0.6L _(S).Furthermore, it is most advantageous that the radius R is substantiallyequal to the radius of the circle which comes in contact with the longsides of the effective image pickup surface.

It is to be noted that in a case where the magnification is fixed in thevicinity of the radius R=0, that is, in the vicinity of the optical axisto perform the correction, a region extended in a radial directionincreases. Therefore, the constitution is slightly disadvantageous inrespect of the number of the pixels, but it is possible to secure aneffect that the zoom lens system can be miniaturized even when the fieldof view is enlarged.

It is to be noted that the correction of the distortion of one image hasbeen described above, but the focal length of the zoom lens systemchanges, and a state of the distortion included in the image changeswith the change of the focal length. Therefore, it is preferable that afocal length zone which requires the correction between a maximum value(the telephoto end) and a minimum value (the wide-angle end) of thefocal length is divided into several focal length zones to correct thedistortion. For example, a correction amount is set so as to obtain acorrection result which substantially satisfies r′(ω)=α·f·tan ω in eachdivided focal length zone in the vicinity of the telephoto end (a statein which the focal length is maximized in each zone), and the distortionof the image can be corrected in the corresponding zone by use of thiscorrection amount. However, in this case, a certain degree of barreltype distortion remains in the resultant image in each divided focallength zone in the wide-angle end (a state in which the focal length isminimized in each zone). To avoid this, if the number of the focallength zones is increased, an amount of the data to be recorded for thecorrection in the recording medium increases. To solve the problem, oneor several coefficients with respect to one or several focal lengthsdifferent from those in the divided focal length zones in the telephotoend and the wide-angle end are calculated beforehand. This coefficientmay be determined based on a simulation or a measurement result of acase where the image pickup apparatus is actually used. Moreover, thecorrection amount is calculated so as to obtain the correction resultwhich substantially satisfies the following condition in the vicinity ofthe telephoto end of each divided focal length zone:r′(ω)=α·f·tan ω.This correction amount may be multiplied by the coefficient for eachfocal length to determine the correction amount in the state of thefocal length.

In addition, in a case where any distortion is not seen in an imageobtained when focused at infinity, the following is established:f=y/tan ω,in which y is a height (an image height) of the image point from theoptical axis, f is a focal length of the image forming system (the zoomlens system in this example), and ω is a half angle of an object view.

In a case where the image forming system has the barrel type distortion,the following results:f>y/tan ω.That is, assuming that the focal length f and the image height y of theimage forming system are constant, a value of ω increases.

Next, as an embodiment of an electronic image pickup apparatus accordingto the present invention, an example of a digital camera will bedescribed.

FIGS. 9 to 11 are conceptual diagrams showing a constitution of adigital camera. FIG. 9 is a front perspective view showing an appearanceof a digital camera 140, FIG. 10 is a back perspective view of thedigital camera, and FIG. 11 is a schematic sectional view showing aninternal constitution of the digital camera.

The digital camera 140 includes a photographing optical system 141having an optical path 142 for photographing, a finder optical system143 having an optical path 144 for a finder, a shutter release button145, a flash lamp 146, a liquid crystal display monitor 147 and thelike. When the shutter release button 145 disposed at an upper portionof the camera 140 is pressed, the photographing is performed through thephotographing optical system 141 in response to the pressed button. Anobject image is formed by the photographing optical system 141 on animage pickup surface of a CCD image sensor 149 via a near infraredcutting filter and an optical low pass filter F. The object imagereceived by the CCD image sensor 149 is displayed as an electronic imagein the liquid crystal display monitor 147 provided at a back surface ofthe camera via processing means 151. This processing means 151 isconnected to recording means 152, and the photographed electronic imagecan be recorded. It is to be noted that this recording means 152 may beintegrated with the processing means 151, or the means may separately bearranged. As the recording means, a memory or a hard disk drive (HDD)incorporated in the digital camera may be used, or an HDD, a memorycard, a DVD or the like detachably attached to the digital camera may beused.

Furthermore, an objective optical system 153 for the finder is disposedalong the optical path 144 for the finder. The object image is formed bythis objective optical system 153 for the finder on a view field frame157 of a Porro prism 155 as an image erecting member. Behind this Porroprism 155, an eyepiece optical system 159 is disposed which guides anerected image into an observer's eyeball E. Cover members 150 aredisposed on an incidence side of the photographing optical system 141and the objective optical system 153 for the finder and an emission sideof the eyepiece optical system 159.

It is to be noted that in an example of FIG. 11, parallel flat platesare arranged as the cover members 150, but lenses having powers may beused. Alternatively, the plates may be omitted.

As a photographing optical system, the zoom lens system shown in FIG. 1Ais used in this example. As apparent from FIG. 11, since an optical pathis bent by the prism P, a size of the zoom lens system in a thicknessdirection of the camera is remarkably small as compared with a length ofthe zoom lens system from an incidence surface to an image surface.Therefore, the digital camera can be thinned.

FIG. 12 is a block diagram of a main part of an internal circuit of thedigital camera 140. It is to be noted that in the following description,the processing means 151 includes, for example, a CDS/ADC section 124, atemporary storage memory 117, an image processing section 118 and thelike, and recording means 152 includes a storage medium section 119 andthe like.

As shown in FIG. 12, the digital camera 140 includes an operatingsection 112, a control section 113 connected to this operating section112, and an image pickup driving circuit 116, the temporary storagememory 117, the image processing section 118, the storage medium section119, a display section 120 and a setting information storage memorysection 121 which are connected to a control signal output port of thecontrol section 113 via buses 114 and 115.

The temporary storage memory 117, the image processing section 118, thestorage medium section 119, the display section 120 and the settinginformation storage memory section 121 are constituted so that they caninput or output data with respect to one another via a bus 122. Theimage pickup driving circuit 116 is connected to the CCD image sensor149 and the CDS/ADC section 124.

The operating section 112 includes various input buttons and switchessuch as the shutter release button, and transmits, to the controlsection, event information input from the outside (a camera user) viathese input buttons and switches.

The control section 113 includes a central processing unit (CPU) and thelike. The section is a circuit in which a program memory (not shown) isincorporated and which controls the whole digital camera 140 in responseto an instruction command input from the camera user via the operatingsection 112 in accordance with a program stored in the program memory.

The CCD image sensor 149 receives the object image formed via thephotographing optical system 141. The CCD image sensor 149 is an imagepickup device which is driven and controlled by the image pickup drivingcircuit 116 and which converts, into an electric signal, a lightquantity of the object image for each pixel to output the signal to theCDS/ADC section 124.

The CDS/ADC section 124 is a circuit which amplifies the electric signaloutput from the CCD image sensor 149 and which subjects the signal toanalog/digital conversion to output, to the temporary storage memory117, video bare data (hereinafter referred to as the raw data) simplysubjected to the amplification and digital conversion.

The temporary storage memory 117 is a buffer including, for example, anSDRAM and the like, and is a memory device in which the raw data outputfrom the CDS/ADC section 124 is temporarily stored. The image processingsection 118 is a circuit which reads the raw data stored in thetemporary storage memory 117 or the storage medium section 119 tosubject the data to various electric image processing includingdistortion correction based on an image quality parameter designated bythe control section 113.

The storage medium section 119 is a control circuit of, for example, anapparatus to which a card or stick type recording medium including aflash memory and the like is detachably attached and in which the rawdata transferred from the temporary storage memory 117 and image datasubjected to image processing by the image processing section 118 arerecorded and retained in the card or stick type flash memory.

The display section 120 includes a liquid crystal display monitor 147and a circuit to display an image, an operation menu and the like in theliquid crystal display monitor 147.

The setting information storage memory section 121 includes an ROMsection in which various image quality parameters are stored beforehand,an RAM section to store the image quality parameter selected from theimage quality parameters read from the ROM section by an input operationof the operating section 112, and a circuit which controls input/outputwith respect to these memories.

In the above-mentioned embodiments, a startup time (a time to extendlenses) to bring the camera into a use state as seen in a collapsiblelens barrel is not required, and photographing can quickly be performed.Since the lenses do not extend or retract with respect to the camera,the constitution is preferable from a viewpoint of water-proof ordust-proof design.

The digital camera has been described above as an embodiment of thepresent invention, but the present invention is applicable to anelectronic image pickup apparatus such as a video camera which forms anobject image with a zoom lens system and receives the image with anelectronic image pickup device such as a CCD image sensor to performphotographing.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention. Rather, the scopeof the invention shall be defined as set forth in the following claimsand their legal equivalents. All such modifications as would be obviousto one skilled in the art are intended to be included within the scopeof the following claims.

What is claimed is:
 1. An electronic image pickup apparatus comprising:a zoom lens system; and an image pickup device which is disposed on animage side of the zoom lens system and which converts an image formed bythe zoom lens system into an electric signal, wherein the zoom lenssystem comprises, in order from an object side, a first lens unit havinga negative refractive power, a second lens unit having a positiverefractive power, a third lens unit having a negative refractive power,and a fourth lens unit having a positive refractive power, the firstlens unit comprising, in order from the object side, a negative lens anda reflective optical element which reflects an optical path, duringzooming from a wide-angle end to a telephoto end, each space between thelens units which are adjacent with each other being changed, the firstlens unit being arranged in a fixed position to the image pickup device,and at least the second lens unit and the third lens unit being moved,wherein the reflective optical element is a prism having a reflectivesurface, and wherein said second lens unit includes a bi-convex lenselement and a cemented lens component disposed on the image side of thebi-convex lens element, the cemented lens component including a positivelens element and a negative lens element, and wherein the third lensunit comprises a single lens component having a negative refractivepower.
 2. The electronic image pickup apparatus according to claim 1,wherein the bi-convex lens element is a most object side lens element inthe second lens unit.
 3. The electronic image pickup apparatus accordingto claim 2, wherein the second lens unit further comprises a secondbi-convex lens element.
 4. The electronic image pickup apparatusaccording to claim 1, wherein the zoom lens system comprises an aperturestop which moves integrally with the second lens unit.
 5. The electronicimage pickup apparatus according to claim 1, wherein the fourth lensunit including a single lens having a positive refractive power, thetotal number of the lenses of the fourth lens unit being one.
 6. Theelectronic image pickup apparatus according to claim 1, wherein the zoomlens system being constituted as a four-unit zoom lens system, thesecond lens unit including, in order from the object side, a pluralityof positive lenses and the negative lens, the negative lens beingcemented to the positive lens disposed on the object side of thenegative lens.
 7. The electronic image pickup apparatus according toclaim 1, wherein the following condition is satisfied:0.4<f2/ft<0.8  (1), in which f2 is a focal length of the second lensunit, and ft is a focal length of the zoom lens system in the telephotoend.
 8. The electronic image pickup apparatus according to claim 1,wherein the following condition is satisfied:1.5<|f1/fw|<3.0  (2), in which f1 is a focal length of the first lensunit, and fw is a focal length of the zoom lens system in the wide-angleend.
 9. The electronic image pickup apparatus according to claim 1,wherein the following condition is satisfied:1.0<|fL1/fw|<2.0  (3), in which fL1 is a focal length fo the negativelens of the first lens unit closes to the object side, and fw is a focallength of the zoom lens system in the wide-angle end.
 10. The electronicimage pickup apparatus according to claim 1, wherein during the zoomingfrom the wide-angle end to the telephoto end, the third lens unit movestoward the object side, and then the moves toward an image surface. 11.The electronic image pickup apparatus according to claim 10, wherein thethird lens unit is arranged closer to the object side in the telephotoend than in the wide-angle end.
 12. The electronic image pickupapparatus according to claim 1, wherein during the zooming from thewide-angle end to the telephoto end, the second lens unit moves towardthe only object side, and has a state in which the second lens unit hasa magnification of −1 while the second lens unit is moving, the thirdlens unit moves toward the object side, and then moves toward an imagesurface, and the fourth lens unit is arranged in a fixed position to theimage pickup device.
 13. The electronic image pickup apparatus accordingto claim 1, wherein the total number of the lenses of the third lensunit is one.
 14. The electronic image pickup apparatus according toclaim 1, wherein the third lens unit comprises a negative lens componentwhich satisfies the following condition and whose concave surface facesthe image side:1.0<(R1+R2)/(R1−R2)<3.0  (4), in which R1 is a paraxial radius ofcurvature of an object-side surface of the negative lens component, andR2 is a paraxial radius of curvature of an image-side surface of thenegative lens component, the lens component being a lens having only twosurfaces of the object-side surface and the image-side surface whichcome in contact with air in the optical path, and being a single lens ora cemented lens.
 15. The electronic image pickup apparatus according toclaim 14, wherein a lens component of the third lens unit is the onlynegative lens component, the image-side surface of the second lens unitis a concave surface, and the object-side surface of the fourth lensunit is a convex surface.
 16. The electronic image pickup apparatusaccording to claim 1, wherein the first lens unit includes one positivelens and one negative lens on an image-surface side of the reflectiveoptical element.
 17. The electronic image pickup apparatus according toclaim 1, wherein the fourth lens unit comprises one positive lenscomponent having an aspherical surface, the total number of lenscomponents of the fourth lens unit is one, and the lens component is alens having only two surfaces of an object-side surface and animage-side surface which come in contact with air in the optical path,and is a single lens or a cemented lens.
 18. The electronic image pickupapparatus according to claim 1, further comprising: a processing sectionwhich performs signal processing to electrically correct a distortion ofthe zoom lens system based on a signal from the image pickup device.